Fuse construction



Aug. 26, 1941. G. F. MCMAHON 2,253,720 A FUSE coNsTRUcTIoN Filed April12, 1940 2 Sheets-Sheet l 'Aug. 26, 1941. G, F. MCMAHON FUSECONSTRUCTION Filed April i2, 1940 2 Sheets-Sheet 2 wW7/////////////////////// 5 7/ ,4 V/ y E v a I @ill/5f ,Patented Auges,1941 UNITED sTATEs PATENT oFFlcE FUSE CONSTRUCTION George F. McMahon,lChicago, Ill., `assigner to Schweitzer & Conrad, Inc., Chicago, lli., acorporation of Delaware Application April 12, 1940, Serial No. 329,258

15 Claims. (Cl. 20G-120) This invention relates generally to circuitinterru'pting apparatus and it has particular relation to fuse links.

An object of this inventionis to secure the insulating tube or sleevevof a fuse link to one of .the link terminals by adhesive means.

Another object of this invention is to provide, asa part of a fuse link,an indicator-which by its absence or presence shows whether or not thefuse link has blown. y

Still another object of this invention is to provide a fuse link withacomposite sleeve the lining and sheath of which have differentcharacteristics. l f l A further object of this inventionis to mount afusible element comprising a tin core and a silver sheath in generallyU-shaped -link terminals.

A still further object of this invention is to surround a fusibleelement comprising a tin core and a silver sheath or tin alone with anarc extinguishing material.

Another object of this invention is to preven loxidation of a tinfusiblev element'surrounded by magnesium borate.

A further object of this invention is to facilitate grasping a terminalof a fuse link for apply. ing it to and removing it from an externalterminal.

I constructions hereinafterset forth, the scope of the applicationofwhichwill be indicated in the appended claims.

For a more complete understanding of the nature and scope -of thisinvention, reference may be had to the following detailed descriptiontaken in connection with the accompanying drawings, in'which: Y

Figure 1 is a view, in side elevation, f one form of cutout in whichthe, fuse links-of the present invention may be employed;

Figures 2A and 2B, taken together, constitute a longitudinal sectionalview showing the details of construction of the fuse tube that isadapted to -be inserted in the cutout shown in Figure 1;

Figure 3 is a view inside elevation, the fuse tube beingshown inysection,-of a fuse link which 1152A and 2B;

Figure 4 is a view in side elevation, the fuse tube being shown insection, of another form of fuse link; l

Figure 5 is a detail sectional view, at an enlarged scale, taken'alongthe line 5-5 of Figure 4;

Figure 6 shows another embodiment of the fuse link; and

'Figure' '7 is a detail sectional view, at an enlarged scale, takenalong the line 1-1 of Figure 6.

Referring now particularly to Figure 1 of the drawings, it will beobserved that the reference character III designates, generally, acutout which may be mounted on a suitable support such as a crossarm IIby means of a suitable clamp I2. A bracket I3 is secured, as shown, tothe clamp I2 and is arranged to support a housing I4, which ispreferably formed of porcelain. At itsl upper end a handle I5 isprovided which may be grasped by the hand of a lineman for removing thefuse tube from the` housing I4.

In Figures 2A and 2B of the drawings the refer-4 louter housing I9,preferably of a phenolic condensation product, such as Bakelite or otherthermosetting or thermoplastic material, and a liner 20 formed, forexample, of fiber or fibrous'` material impregnated with magnesiumborate. At its upper end the fuse tube I8 is provided with a lineterminal 2l which is arranged to be con- Il, Figure 1. At its upper endthe` terminal 2l is threaded, as indicated at 22, for receiving thehandle I5, Figure 1.

Within the fuse tube I8 there is provided a spring and cable assemblythat is shown generally at 2l. Thisy assembly comprises a c oil tensionspring 25 within whichthere is positioned a flexible conductor or cable26.' ,'Ihespring 25 and cable 26 are secured at2 their upper ends to aspring and cable fastener 21 which` has a flanged head that restsagainst the upper end of the terminal 2 i, as shown. The lower endsofthe spring 25 and cable 2B are secured to a spring and 'cable fastener28 which constitute this an external terminal and which has a knurledsection 29 to facili- 'tate its being gripped by a suitable tool such asa pair of pliers for application of or removal from a terminal,v showngenerally at 30, of a replaceable fuse link, shown generally at 3l. Thefuse link 3| is provided with' a'tube or sleeve 32 of insulatingmaterial and it has projecting out of its lower end a iexible lead 33onto which a wedge shaped terminal 34 is deformed for intertting betweenupstanding ears 35 of a lower line terminal 36 which is mounted at thelower end of the fuse tube I8.

The details of construction of the cutout previously described aregenerally the same as those illustrated and described in Ramsey PatentNo. 2,108,993. It is to the particular details of the construction ofthe fuse link 3l that the present invention is directed.

In Figure 3 of .the drawings, certain of the novel features embodied inthe fuse link construction of the present invention are shown. It willbe observed that the fuse tube terminal 30 is generally rod-like incharacter and therefore that it is relatively infusible. Its upper endportion 38 is threaded for attachment to the spring and cable fastener28. Just below the threaded portion 38 there is provided a knurledportion 39 for receiving a suitable tool such as a pair of pliers inorder to facilitate grasping the terminal 30 for application to orremoval from the spring and cable fastener 28.

Immediately below the knurled portion 39 there is provided a generallycylindrical portion 40 to which the tube or sleeve 32 is secured bymeans of a suitable adhesive 4I. Adhesive material is employed forholding the tube or sleeve 32 in place instead of a pin, as shown inFigures 4 and 6 hereinafter described, in order to reduce the outsidediameter of the assembly so that the fuse link can be inserted in a fusetube having an internal diameter only slightly larger than the outsidediameter of the fuse link.

The tube or sleeve 32 is preferably formed of rolled paper impregnatedwith magnesium borate as disclosed in the copending application ofMcMahon, Serial No. 266,991, filed April 10,

The lower end portion 42 oi' the terminal 36 is generally tubular inconstruction and is deformed onto the upper ends of fusible and strainelements 43 and 44. The fusible element 43 may be formed of non-ferrousmetal such as silver, copper, aluminum, cadmium, zinc or alloys of thesemetals, while the strain element 44 is formed of a high strength alloy.such as a nickel chromium alloy. The lower end portions of the fusibleand strain elements 43 and 44 are secured by having the upper endportion 45 of a generally rod-like terminal 46 deformed thereon. Thelower end of the terminal 46 is generally tubular in character and asindicated at 41 it is deformed onto the upper end of the flexible lead33. The upper end portion 50 of the wedge-shaped terminal 34 is deformedonto the lower end of the flexible lead 33.

It is desirable that a readily visible indicator be provided forindicating by its absence or presence whether or not the fuse link 3lhas blown. For this purpose the wedge-shaped terminal 34 is providedwith a generally tubular section I which is deformed, as indicated at52, onto` the upper end of an elongated insulator member 53 whichconstitutes an indicator member. 'I'he member 53 is, preferably formedof a white moulded plastic so that it will be readily visible from theground. As shown in Figure l, theindicator member 53 projects asubstantial distance below the lower end of the housing I4 so that it isreadily visible. At its iower end the indicator member 53 is providedwith grooves 54 for receiving a pull-up string for facilitating there-fusing of the fuse tube I8.

In operation, when the fusible and strain elements 43 and 44 of the fuselink 3I blow, the spring 25.is no longer restrained. Accordingly, itretracts the upper fuse link terminal 30 and tube or sleeve 32 securedthereto into the tube I8, thereby elongating the arc formed between ytherelatively infusible terminals 30 and 46 for extinguishing the same. Dueto the heat of the arc thus formed, water may be evolved from the innersurface of the tube or sleeve 32 and it further assists in extinguishingthe arc. Since the lower fuse link vterminal 46 is no longer restrainedyit and the indicator member 53 drop out or are blown out of their normalpositions at the lower end of the tube I8. It will thus be apparent thatthe presence of the indicator member 53 at the lower end of the housingI4 shows that the fuse link 3| has not blown. However, its absenceindicates that it has blown and that the cutout should be re-fused.

In Figure 4 of the drawings, another embodiment of the fuse linkconstruction is shown generally at 51. The link 51 is provided with anupper relatively infusible terminal that is shown, generally, at 58. Itsupper end portion is threaded as indicated at 59 for attachment to thespring and cable fastener 28, Figure 2B, or for receiving a flangedtting 60 for mounting in other types of cutouts, such as an expulsiontype of cutout. Below the threaded portion 59 there is provided aknurled portion 6I for facilitating the securing of the .terminal 58 inposition or removing it therefrom, as previously described.

Below the knurled portion 6I there is provided a longitudinally knurledportion 62 over which a composite tube or sleeve, shown generally at 63,is positioned. This composite sleeve 63'may be secured to lthe terminal58 by means of a transversely extending pin or screw 64.

The composite sleeve 63 preferably comprises a liner 65 formed of rolledpaper impregnated with magnesium borate and an outer sheath 66 formed offiber. The magnesium borate in the li-ner 65 evolves a considerableamount of water i vapor under the heat of an arc for assisting inextinguishing it while the fiber sheath 66 serves to reinforce the liner65 and protects the same in handling. y The ber sheath 66 also possessesarc extinguishing properties but to a lesser degree than magnesiumborate.

The lower portion 68 of the upper fuse link terminal 58 is of al tubularconstruction and is deformed onto the upper end of a strain element 69which, as previously indicated, may be formed of a nickel alloy wire. Indeforming the lower portion 68 of the terminal 58, a generally U- shapedfusible element receiving portion is formed and in this, one end of afusible element, sho'vs'm generally at 10, is soldered, as indicated at4 As shown in Figure 5 of the drawings, the fusible element 16 comprisesa core 12, formed principally of tin, and a sheath 13, formedprincipally of silver. The silver-tin fusible element is more fullydescribed in the copending application of Triplett, Serial No. 144,789,filed May 26,

in construction and it is deformed onto the lower end of the strainelement 69 for fastening thereto. In deforming the portion 14 agenerally U- shaped fusible element receiving portion is provided, asdescribed in the portion 68 and in it the lower end of the fusibleelement 10 is positioned and secured in place by solder 16.

The generally U-shapedportions 68 and 14 of the fuse link terminals 58and 15 form a cradle constructiomwhich isv described in more detail inTriplett et a1. Patent No; 2,174,767.

The lower fuse link terminal 15 is deformed onto one end of a flexiblelead 11 which extends "cured to the corresponding terminal, as will bereadily understood.

In Figure 6 of the drawings, the fuse link shown generally at 80 -lsgenerally similar lin construction to the fuse link 51, shown in Figure4, and described hereinbefore. However, in the fuse link 88 the fusibleelement,.shown generally at 8|, is composed of non-ferrous metal such ascopper, cadmium, aluminum, zinc or alloys of the same, as indicated at82 in Figure 7 of the drawings.

With a view to preventing oxidation of the tin core 82, or of othercores consisting of readily oxidizable metals, the core is provided witha baked enamel sheath 83 which is capable of withstanding without injurytheh'eat generated by the core 82 substantially up to or just below itsmelting point. Preferably, the enamel sheath83 is formed by spraying onthe tin core 82 after it has been assembled in the terminals 58 and 15a1 lacquer which can be obtained in theI open market under the tradename of Duranite.

' After the spraying operation has been completed,

the assembly is placed in an oven and baked at 250 F. to 275 F. forabout one hour in order to harden and polymerize the resin in thelacquer. f Fuse links of the .type herein disclosed are particularlywell adapted to clear low current faults at low power factor and highrecovery voltage. It has been found that operationunder these conditionsusing the present invention is superior to results obtained when othermaterials such as liber are used.

Since certain further changes may be made in the foregoing constructionsand different embodiments of the invention can be imade withoutdeparting from the scope thereof, it vis intended that allv matter'shown in the accompanying drawings and described hereinbefore shallbefiniterpreted as illustrative and not in a limiting sense. A

What is claimed as new is:

1. In a fuse, in combination, a pair of terminal means and fusiblemeans` interconnecting the same, one of said terminal means beingrod-likel in character and adapted to be connected to an externalterminal at one end and to said fusible means at the other end, asleeve-of insulating material containing magnesium borate telescopicallyrelated to said pair of terminal means, and

2. A fuse linkV comprising, in combination, a

pair of terminal means adapted to be connected to line terminals andinterconnected by fusible means, an elongated insulator member acting asan indicator, and a sleeve vconstituting an extension of one of saidterminal means and deformed onto one end of said elongated insulator.

3. In a fuse, in combination, a pair of spaced relatively infusible'terminals, fusible means interconnecting said terminals, and va.composite insulating sleeve surrounding'said fusible means having asheath formed of are extinguishing material and a liner closely fittingtherewith and carrying magnesium borate.

4. In a fuse, in combination, a pair of `spaced relatively infusibleterminals, fusible means interconnecting said terminals, and a compositeinsulating sleeve surrounding said fusible means having a fiber sheathand a -liner extending throughout its entire length and carryingmagnesium borate.

5. In a fuse, in combination, a. pair ofspaced" relatively infusibleterminals, fusible means interconnecting said terminals, a compositeinsulating sleeve telescopically related to said terminals and having afiber sheath and a liner c arrying magnesium borate, and means forsecuring said composite sleeve to at ,least one of said terminals.

6. In a fuse, in combination, a pairv of spaced relatively infusibleterminals, fusible means interconnecting said terminals, a compositeinsulating sleeve telescopically related to said terminals and having aber sheath and a liner carrying magnesium borate, and means for securingsaid composite sleeve Ito one of said terminals, the other terminalbeing free to move out of said sleeve on blowing of said fusible means.

7, In a fuse, in combination, a pair of terminal members having endportions extending toward each other, said end portions having laterallyopening aligned U-shaped fusible element receiving portions, strainmeans interconnecting said terminal members, a fusible elementcomprising a tin core and a silver sheath secured tubular end portions;-said tubular end portions' being -deformed in such manner as to formsubstantially U-shaped fusible element receiving portions, a fusibleelement comprising a tin core and a silver sheath also interconnectingsaid terminals with its ends disposed in said U- shaped fusible elementreceiving portions, and a sleeve of insulating material secured to atleast one of said'terminals and surrounding said fusible element andcarrying magnesium bor-ate in such position that it is exposed Yto theheat of the arc formed on blowing of said fusible element.

9. In a fuse, in combination, a pair of spaced relatively infusibleterminals, la fusible element interconnecting said terminals comprisinga core composed principally of tin and a sheath composed principally ofsilver; and a sleeve of insulating material carrying magnesium boratelsurrounding said fusible element.

10. In a fuse,in combination, a pair of spaced relatively infusibleterminals, a fusible element interconnecting said terminals comprising acore composed principally of tin and a sheath composed principally oi'silver, and a sleeve of ce1- lulosic material impregnated with magnesiumborate surrounding said fusible element.

11. In a fuse, in combination, a pair of spaced relatively infusibleterminals, a fusible element interconnecting said terminals comprising acore composed principally of ltin and a sheath composed principally ofsilver, and a rolled paper sleeve impregnated with magnesium boratesurrounding said fusible element.

12, In a fuse, in combination, a pair of spaced relatively infuslbleterminals, a fusible element selected from the class consisting of tin,copper, aluminum, cadmium and zinc interconnecting said terminals, and asleeve of insulating material carrying magnesium borate surrounding saidfusible element.

13. In a fuse, in combination, a pair of spaced relatively infusibleterminals, a fusible element selected from the class consisting of tin,copper, aluminum, cadmium and zinc interconnecting said terminals, andasleeve'of cellulosic mate- :rial impregnated with magnesium bor-atesurrounding said fusible element.

14. In a fuse, in combination, a pair of spaced relatively infusrlbleterminals, a fusible element selected from fthe class consisting of tin,copper, aluminum, cadmium and zinc interconnecting said terminals, and arolled paper sleeve impregnated with magnesium Aborate surrounding saidfusible element.

15. In a fuse, in combination, a pair of spaced relatively infusibleterminals, a fusible element composed o1' an oxidizable metalinterconnecting said terminals, an enamel coating on said fusibleelement to prevent oxidation thereof, and a sleeve of insulatingmaterial carrying magnesium borate surrounding said fusible element.

GEORGE F. MCM'AHON.

